1. Field of the Invention
This invention relates generally to architectural transparencies and, more particularly, to tempered and non-tempered coated glass substrates (temperable and non-temperable coatings) having similar optical characteristics.
2. Technical Considerations
As will be appreciated by one skilled in the architectural art, glass is used typically in either a tempered form or a non-tempered (annealed) form, depending upon the desired final use of the glass. For annealed glass, the glass is heated to the annealing point of the glass and then allowed to slowly cool to below the strain point of the glass. The annealed glass can be cut to desired final dimensions, such as for a door, window, and the like. For even stronger glass, tempering is used. In tempering, glass is heated above the annealing point of the glass and then rapidly cooled, such as by directing a cooling medium at the glass, to provide the glass with an exterior compressive force and an interior tensile force. Tempered glass is much stronger than annealed glass and is used were safety is an important factor. However, unlike annealed glass, tempered glass cannot be cut or it will shatter. Therefore, where tempered glass is desired, the glass must be cut to the desired final dimensions before tempering.
Solar control coatings are known in the field of architectural transparencies. Solar control coatings block or filter selected ranges of electromagnetic radiation, such as in the solar infrared or solar ultraviolet ranges, to reduce the amount of solar energy entering the building. This reduction of solar energy transmittance helps reduce the load on the cooling units of the building. In some architectural applications, it may be desirable to have a reflective outer surface so as to decrease visibility into the building to retain as much privacy as possible, while still allowing visible light to enter the building and also allowing the workers inside the building to see out.
A conventional building may require both annealed (non-tempered) and tempered glass pieces with solar control coatings. For example, annealed glass with a solar control coating may be used on the lower floors while tempered glass with a solar control coating is used on the upper floors for increased safety. Both the coated annealed glass and the coated tempered glass should have the same or very similar optical characteristics so that the building maintains the same overall aesthetic appearance. This causes a problem for coated glass manufacturers.
Most glass manufacturers sell large sheets of coated annealed glass to glass suppliers. The suppliers cut the glass sheets to desired dimensions, such as for doors, windows, etc., and sell the cut glass to a customer. However, for tempered glass orders, the glass suppliers must cut the coated annealed large glass sheet to smaller pieces of a desired final dimension and then temper the smaller coated glass pieces (i.e. subjecting the coating to additional heating and rapid cooling steps). Tempering the coated glass pieces can result in the tempered products having different color or optical characteristics than the original annealed products due to changes in the coating caused by the extra heating and rapid cooling steps required to temper the glass. This difference in color or other optical properties, such as transmittance or reflectance, between the coated tempered glass and the coated annealed glass is not desirable if the annealed and tempered products are to be used in the same building. Also, the coating on the tempered product may become hazy due to the high temperatures and rapid cooling required for the tempering process. This haze is aesthetically undesirable.
It would be desirable for glass manufacturers to provide glass suppliers with at least two types of coated (annealed) glass sheets, one that could be cut and sold as is for annealed applications (i.e. having a non-temperable coating) and another that could be cut into smaller pieces and then subsequently tempered (temperable coating) but which, after tempering, has the same or substantially the same aesthetic and optical characteristics as the non-tempered glass so that the two types of coated glass could be used in the same building.